Tuesday, 28 February 2012

Shear Coaxial Injector - Constructing the Prototype Injector for Research

The previous post gave details of the design and the dimensions of the research injector. I will now go on to describe its' construction. As mentioned, I decided to make the body of the unit from BS230M07 steel. This is a free cutting mild steel. I know a lot of my readers are in the United States, so for their benefit the nearest equivalent would be AISI 1213.

The centre fuel post started out as a 316 stainless steel M8 x 50mm hex head screw. I manufactured a threaded bush to hold this and then faced the end:-

Next I centre drilled the end of the screw and then generated the 1.85mm injection hole. I had to use a cobalt drill on the hard 316 stainless steel:-

The next thing to do was to set the screw up and turn the thread back to leave 15mm of it remaining:-

Once this step was completed the fuel post was reversed in the chuck and a 4mm fuel feeder hole was drilled for approximately 40mm:-

Once the fuel post was complete, I started bringing the body of the unit to size. There was no need to have the full chamber flange diameter for the research unit:-

Once the unit was to size it was time to start boring the various diameters required:-

First of all a 6.8mm hole was put right through, this is the tapping drill for an M8 x 1.25 thread:-

Next a flat bottomed hole of diameter 14mm x 25mm deep was generated using a slot drill in the tailstock. I found 14.5mm to be the optimum tapping drill size for a 3/8 inch BSPT fitting, without reaming the hole. The hole was bored to final size:-

Next step was to tap the 6.8mm hole to M8 for 15mm to accept the fuel post:-

The 3/8 inch BSPT thread was then generated for the fuel inlet fitting:-

Then the part was reversed and parted to length.The 6.8mm hole in the end of the unit was then bored out to the design diameter of 8.17mm, for 35mm:-

The body of the unit was now almost complete. After lathe clean up cuts, the next step was to drill and tap the 90 degree hole to 1/4 inch BSPT, into the annulus bore for the oxygen inlet:-

The unit was then assembled using an M8 viton/stainless steel bonded washer to seal the fuel post bolt. It was now ready for testing to commence. The study of CR-120936 and the design of the research injector took place between June and August 2009. The construction work shown in this post took place in June of 2010. In the next post I will look at the first tests of this research injector.

About this blog

This blog describes the research, design and construction of a Liquid Rocket Engine.
As such it will include information regarding the design and construction of rocket engine components.
This will encompass theoretical and performance concerns, as well as machining, welding and manufacturing techniques used to overcome the various problems encountered.
In addition, my interests in this direction include control and data acquisition. So there will be posts regarding electronic systems and microcontrollers.
It is my hope that as well as being of interest to the rocket engine community, it should also become a repository of general amateur engineering information.
I was inspired to create a blog by the groundswell of interest that I have had in my project from people I have met. I have found that their reactions tend to go from perplexity to enthusiasm rapidly! The main question most people have is not to do with the technical obstacle to be overcome. Most of those who have asked me about my project have wanted to know "Why are you doing this?" So I will try to give some answers to this and to explore my motivation to think, research, create and construct.